The present invention relates to silver-containing compositions and more particularly to photocurable silver-containing compositions, to methods for making and applying a photocurable silver-containing compositions as a coating on a substrate.
There are many instances in which it is necessary or desirable to apply a coating, plating or layer of silver or a silver-containing compound to a substrate. Examples of such applications would include electrode plating for switches such as those used on pressure-sensitive switches or control panels, for example, as are used on appliances such as microwave ovens, conventional ovens, and the like. Such silver plating also is commonly used in the semiconductor fabrication arts to apply silver metalizations on silicon or germanium semiconductor wafers. Other examples of such substrates include, without limitation, such things as polyesters, polycarbonates, vinyls, ceramics, glass, and the like.
The predominant approach heretofore used in applying silver to substrates has involved using a solvent-based silver solution to the substrate, and chemically or thermally curing the solution to evaporate the solvent. This leaves the solid silver plating on the substrate.
This conventional approach is disadvantageous in a number of respects. Of perhaps the greatest concern is the fact that the solvents currently used for this purpose are toxic. They require special handling and disposal facilities and techniques, and correspondingly increase inefficiencies and costs. Even while observing these special handling techniques, they present hazards to workers using these toxic materials. The solvent-based compositions and methods also are disadvantageous in that it can be difficult to predict the uniformity and thickness of the resultant silver plating after the solvent has evaporated. This leads to quality and performance variations.
Accordingly, an object of the present invention is to provide a silver composition and method in which silver can be disposed on a substrate without requiring a toxic solvent.
Another object of the invention is to provide a silver composition and method in which disposition of the silver layer can be done more quickly and efficiently than prior art solvent-based techniques.
Another object of the invention is to provide a silver composition and method in which a silver coating may be created which has more predictable and uniform layer thickness relative to prior art solvent-based systems.
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, a silver composition is provided for deposition as a coating, plating, film or layer on a substrate. The terms coating, plating, film and layer in the context of this document are used to refer generally to a covering on the surface of a substrate, which covering may be of a variety of thicknesses depending on the application and the design goals.
In accordance with one aspect of the invention, a photocurable silver composition is provided. The silver composition comprises a photocurable organic mixture, a photoinitiator, a silver powder, and a silver flake composition. The silver flake composition is present in an amount of at least 20% of the weight of the silver powder present in the composition. Incorporation of silver flake composition in an amount of at least 20% results in films with superior conductivity. Resistivities as low as 0.03 ohm/sq at 1 mil are achieved.
The photocurable silver composition preferably comprises an aliphatic acrylated oligomer, wherein the aliphatic acrylated oligomer is present in an amount of about 3% to 8% based on the weight of the silver composition. All percentages of the silver composition as expressed in this document, unless otherwise stated, refer to the mass percentage of the stated component to the total mass of the silver composition in its fluid uncured state at standard temperature and pressure.
The silver composition also preferably comprises an acrylated epoxy oligomer, wherein the acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition.
The silver composition also preferably comprises an isobornyl acrylate monomer in an amount of about 4% to 8% of the silver composition, a photoinitiator in an amount of about 3% to 6% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a silver powder in an amount of about 50% to 60% of the silver composition, and a silver flake composition in an amount of about 25% to 35% of the silver composition.
In accordance with this aspect of the invention, the aliphatic acrylated oligomer preferably comprises a urethane oligomer. In presently preferred versions of the silver composition, the aliphatic acrylated oligomer is present in an amount of about 8% of the silver composition.
The acrylated epoxy oligomer is preferably present in an amount of about 3% of the silver composition. The isobornyl acrylate monomer is preferably present in an amount of about 5% of the silver composition. The photoinitiator is preferably present in an amount of about 5% of the silver composition. The flow promoting agent is preferably present in an amount of about 1% of the silver composition.
In presently preferred embodiments according to this aspect of the invention, the silver powder preferably but optionally is present in an amount of about 52% of the silver composition. In these preferred embodiments, the silver powder has a particle size range of about 5 microns to about 15 microns. In a more preferred embodiment, the silver powder has a particle distribution such that about 5% to 20% of the particles have a particle size of less than about 4.7 microns, about 30% to 60% of the particles have a particle size of less than about 7.6 microns, and about 70% to 95% of the particles have a particle size of less than about 14.9 microns. In the most preferred embodiment, the silver powder has a particle distribution such that about 10% of the particles have a particle size of less than about 4.7 microns, about 50% of the particles have a particle size of less than about 7.6 microns, and about 90% of the particles have a particle size of less than about 14.9 microns.
According to the presently preferred embodiments, the silver flake is present in an amount of about 30% of the silver composition. Preferably the silver flake has a particle size range of about 5 microns to about 32 microns. The silver flake preferably has a flake distribution such that about 10% of the particles have a particle size of less than about 5.5 microns, about 50% of the particles have a particle size of less than about 12.5 microns, and about 90% of the particles have a particle size of less than about 32.0 microns.
In a further refinement of the presently preferred embodiment, an adhesion promoter is present in about 1 to 4% of the silver composition. This further refinement improves adhesion to substrates coated with transparent conductors such as indium tin oxide (ITO).
In accordance with another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable of shielding electromagnetic radiation is provided. This embodiment is preferably applied to a substrate by spraying. The silver composition comprises an acrylated epoxy oligomer, wherein the acrylated epoxy oligomer is present in an amount of about 2% to 8% of the silver composition. The silver composition preferably comprises an isobornyl acrylate monomer in an amount of about 15% to 30% of the silver composition, an photoinitiator in an amount of about 3% to 7% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a silver powder in an amount of about 20% to 40% of the silver composition, and a silver flake composition in an amount of about 20% to 40% of the silver composition.
In accordance with another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable of forming resistive links on circuit boards is provided. This embodiment of the invention preferably does not contain any urethane The silver composition comprises an acrylated epoxy oligomer having, wherein the acrylated epoxy oligomer is present in an amount of about 16% to 20% of the silver composition. The silver composition also comprises an isobornyl acrylate monomer in an amount of about 8% to 14% of the silver composition, an photoinitiator in an amount of about 4% to 8% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a silver powder in an amount of about 25% to 38% of the silver composition, and a silver flake composition in an amount of about 20% to 40% of the silver composition.
In accordance with yet another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable resistive links on circuit boards is provided. This embodiment contains urethane. The silver composition comprises an aliphatic acrylated oligomer (a urethane), wherein the aliphatic acrylated oligomer is present in an amount of about 7% to 11% of the silver composition. The silver composition further comprises an acrylated epoxy oligomer, wherein the acrylated epoxy oligomer is present in an amount of about 1% to 4% of the silver composition. The silver composition also comprises an isobornyl acrylate monomer in an amount of about 12% to 25% of the silver composition, a photoinitiator in an amount of about 2% to 4% of the silver composition, a flow promoting agent in an amount of about 0.0% to 4% of the silver composition, an antimony tin oxide powder in an amount of 7% to 19%, a silver powder in an amount of about 24% to 30% of the silver composition, and a silver flake composition in an amount of about 15% to 30% of the silver composition. In a further refinement of this embodiment, the silver composition further comprises a polyacrylic oligomer/acrylate monomer blend in an amount of about 5% to 10%.
In accordance with yet another aspect of the invention, a photocurable silver composition suitable for producing a coating that is capable black colored resistive links on circuit boards is provided. The silver composition comprises an aliphatic acrylated oligomer, wherein the aliphatic acrylated oligomer is present in an amount of about 7% to 11% of the silver composition The silver composition further comprises an acrylated epoxy oligomer having, wherein the acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition. The silver composition also comprises an isobornyl acrylate monomer in an amount of about 10% to 14% of the silver composition, a photoinitiator in an amount of about 13% to 15% of the silver composition, a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, a conductive carbon black powder in an amount of 5% to 12%, a wetting agent in an amount of about 0.5 to 3% of the silver composition, a silver powder in an amount of about 30% to 40% of the silver composition, and a silver flake composition in an amount of about 15% to 25% of the silver composition.
In accordance with another aspect of the invention, a method is provided for making a photocurable silver composition. The method comprises a first step of combining and mixing an isobornyl acrylate monomer and a photoinitiator to create a first mixture. The isobornyl acrylate monomer is present in an amount of about 4% to 8% of the silver composition, and the photoinitiator is present in an amount of about 3% to 6% of the silver composition.
The method includes a second step of combining and mixing an aliphatic acrylated oligomer and an acrylated epoxy oligomer to create a second mixture. The aliphatic acrylated oligomer is present in an amount of about 3% to 8% of the silver composition and the acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition.
The method includes a third step of combining and mixing a silver powder and a silver flake composition to create a third mixture. The silver powder is present in an amount of about 50% to 60% of the silver composition and the silver flake composition is present in an amount of about 25% to 35% of the silver composition.
The method further includes a fourth step of combining and mixing a flow promoting agent in an amount of about 0.1% to 2% of the silver composition, and a fifth step of combining the first, second, third and fourth mixtures to create the silver composition.
Preferably, but optionally, the first, second, third and fourth steps are performed sequentially. The method in its various forms may be carried out on a batch basis, for example, in a mixing vessel or similar process equipment suitable for batch processing. It may also be carried out in other forms, for example, such as continuous flow regimes.
In accordance with another aspect of the invention, another method is provided for making a photocurable silver composition. This method comprises a first step of combining and mixing an isobornyl acrylate monomer and a photoinitiator to create a first composition, wherein the isobornyl acrylate monomer is present in an amount of about 4% to 8% of the silver composition, and the photoinitiator is present in an amount of about 3% to 6% of the silver composition. This method also includes a second step of combining with the first composition and mixing an aliphatic acrylated oligomer and an acrylated epoxy oligomer to create a second mixture. The aliphatic acrylated oligomer is present in an amount of about 3% to 8% of the silver composition and the acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition.
The method further includes a third step of combining with the second composition and mixing a silver powder and a silver flake composition to create a third composition. The silver powder is present in an amount of about 50% to 60% of the silver composition and the silver flake composition is present in an amount of about 25% to 35% of the silver composition.
The method still further includes a fourth step of combining with the third composition and mixing a flow promoting agent in an amount of about 0.1% to 2% of the silver composition.
This method also may be carried out in a batch format, for example, in a mixing vessel or series of mixing vessels, in a continuous flow regime, or in some combination.
In accordance with yet another aspect of the invention a method is provided for depositing a silver coating on a substrate. The method comprises a first step of applying to the substrate a silver-containing fluid-phase composition (xe2x80x9csilver compositionxe2x80x9d). The silver composition comprises an aliphatic acrylated oligomer, wherein the aliphatic acrylated oligomer is present in an amount of about 3% to 8% of the silver composition. The silver composition further includes an acrylated epoxy oligomer. The acrylated epoxy oligomer is present in an amount of about 2% to 4% of the silver composition. The silver composition also includes an isobornyl acrylate monomer in an amount of about 4% to 8% of the silver composition, a photoinitiator in an amount of about 3% to 6% of the silver composition, and a flow promoting agent in an amount of about 0.1% to 2% of the silver composition. The silver composition further includes a silver powder in an amount of about 50% to 60% of the silver composition, and a silver flake composition in an amount of about 25% to 35% of the silver composition.
The method also includes a second step of illuminating the silver composition on the substrate with light of a wavelength suitable to cause the silver composition to cure into the silver coating. Preferably light will have a wavelength in the ultraviolet region of the electromagnetic spectrum.
In accordance with this method, the silver composition can be selectively deposited on the substrate at specific locations where silver plating is desired. It need not be applied to the entire substrate. It is thus possible, for example, to use the silver coating thus created as metalizations on semiconductor wafers, printed circuit boards, pressure sensitive or pressure activated switches, and the like.
According to another aspect of the invention, a method is provided for preparing a liquid-phase silver-containing composition for use in providing a silver-containing coating or plating on a substrate. The presently preferred version of the method includes preparing the composition as identified immediately above. The method in broad terms includes a first step of combining and mixing the monomer and the photoinitiator in a mixing vessel, a second step of adding to the mixing vessel and blending in the urethane and the epoxy, a third step of adding to the mixing vessel and blending in the silver powder and the silver flake, and a forth step of adding to the mixing vessel and blending in the flow agent.
Silver Compositions
Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventor.
In accordance with one aspect of the invention, a presently preferred photocurable silver composition (xe2x80x9csilver compositionxe2x80x9d) is provided. In this preferred embodiment, the silver composition includes an aliphatic acrylated oligomer. The aliphatic acrylated oligomer is present in an amount of about 3% to 8%, and preferably about 8%, of the silver composition. The aliphatic acrylated oligomer preferably comprises a urethane oligomer. Suitable aliphatic acrylated oligomers include Radcure Ebecryl 244, Ebecryl 264 and Ebecryl 284 urethanes, commercially available from Radcure UCB Corp. of Smyrna, Ga.; Sartomer CN961, CN963, CN964, CN 966, CN982 and CN 983, commercially available from Sartomer Corp. of Exton, Pa.; TAB FAIRAD 8010, 8179, 8205, 8210, 8216, 8264, M-E-15, UVU-316, commercially available from TAB Chemicals of Chicago, Ill.; and Echo Resin ALU-303, commercially available from Echo Resins of Versaille, Mo.; and Genomer 4652, commercially available from Rahn Radiation Curing of Aurora, Ill. The preferred aliphatic acrylated oligomers include Ebecryl 264 and Ebecryl 284. Ebecryl 264 is an aliphatic urethane triacrylate supplied as an 85% solution in hexandiol diacrylate. Ebecryl 284 is aliphatic urethane diacrylate of 1200 molecular weight diluted with 1,6-hexandiol diacrylate. It is obvious to one skilled in the art that combinations of these materials may also be employed herein.
This preferred silver composition further includes an acrylated epoxy oligomer. The acrylated epoxy oligomer is present in an amount of about 2% to 4%, and preferably about 3%, of the silver composition. Suitable acrylated epoxy oligomers include Radcure Ebecryl 3603, commercially available from Radcure UCB Corp.; Sartomer CN120 and CN124, commercially available from Sartomer Corp.; and Echo Resin TME 9310 and 9345, commercially available from Echo Resins. The preferred acrylated epoxy oligomer is Ebecryl 3603, which tri-functional acrylated epoxy novolac. Combinations of these materials may also be employed herein.
The preferred silver composition also includes an isobornyl acrylate monomer in an amount of about 4% to 8%, and preferably about 5%, of the silver composition. Suitable isobornyl acrylate monomers include Sartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commercially available from Radcure Corp.; IBOA and IBOMA, commercially available from CPS Chemical; and Genomer 1121, commercially available from Rahn Radiation Curing. Preferred isobornyl acrylate monomers include Sartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commercially available from Radcure Corp.; IBOA AND IBOMA, commercially available from CPS Chemical; and Genomer 1121, commercially available from Rahn Radiation Curing.
This preferred silver composition also includes a photoinitiator in an amount of about 3% to 6%, and preferably about 4%, of the silver composition. Suitable photoinitiators include Irgacure 184 (1-hydroxycyclohexyl phenyl ketone), 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369 (2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500 (the combination of 1-hydroxy cyclohexyl phenyl ketone and benzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (the combination of bis(2,6-dimethoxybenzoyl-2,4-,4-trimethyl pentyl phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), Ciba-Geigy 1700, and DAROCUR 1173 (2-hydroxy-2-methyl-1phenyl-1-propane) and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), available commercially from Ciba-Geigy Corp., Tarrytown, N.Y.; CYRACURE UVI-6974 (mixed triaryl sulfonium hexafluoroantimonate salts) and UVI-6990 (mixed triaryl sulfonium hexafluorophosphate salts) available commercially from Union Carbide Chemicals and Plastics Co. Inc., Danbury, Conn.; and Genocure CQ, Genocure BOK, and GenocureMBF, commercially available from Rahn Radiation Curing. The preferred photoinitiator is Irgacure 1700 commercially available from Ciba-Geigy of Tarrytown, N.Y.
The preferred silver composition still further includes a flow promoting agent in an amount of about 0.1% to 2%, and preferably about 1.0%, of the silver composition. Suitable flow promoting agents include Genorad 17, commercially available from Rahn Radiation Curing; and Modaflow, commercially available from Monsanto Chemical Co., St. Louis, Mo. The preferred flow promoting agent is Modaflow which is an ethyl acrylate and 2-ethylhexyl acrylate copolymer that improves the flow of the composition. Combinations of these materials may also be employed herein.
The preferred silver composition also includes a silver powder in an amount of about 50% to 60%, and preferably about 52%, of the silver composition. The silver powder comprises a plurality of particles. In this preferred silver composition, the silver powder has a particle size range for these particles of about 5 microns to about 15 microns. In some embodiments, the silver powder has a particle size range of about 4.7 microns to about 14.9 microns. Preferably, the silver powder particles have a particle size distribution wherein about 10% of the particles have a particle size of less than about 4.7 microns, about 50% of the particles have a particle size of less than about 7.6 microns, and about 90% of the particles have a particle size of less than about 14.9 microns. The preferred silver powders are Silver Powder EG-ED and Silver Powder C-ED commercially available from Degussa Corp. of South Plainfield, N.J.
The preferred silver composition further includes a silver flake composition in an amount of about 25% to 35%, and preferably about 30%, of the silver composition. The silver flake composition comprises a plurality of flakes which comprise, and which preferably consist essentially of, silver. The silver flake composition according to this embodiment has a particle size range of about 5 microns to about 32 microns. More preferably, the silver flake composition has a particle size range of about 5.5 microns to about 32.0 microns. The silver flake particle size distribution preferably is such that about 10% of the particles have a particle size of less than about 5.5 microns, about 50% of the particles have a particle size of less than about 12.5 microns, and about 90% of the particles have a particle size of less than about 32.0 microns. The preferred silver flake compositions are Silver Flake #25, Silver Flake #1, and Silver Flake #7A commercially available from Degussa Corp. of South Plainfield, N.J.